Understanding the regulation of cell migration is essential to the fields of developmental biology, immunology and cancer biology. However we lack a fundamental understanding1 of the strategies employed by migrating cells in vivo. The long-term goal of this proposal is to use Drosophila germ cell migration as an in vivo system to study cell migration and invasive behavior. Tre1 is a G-protein coupled receptor (GPCR) that is required specifically for germ cells to migrate through the posterior midgut primordium. Our hypothesis is that Tre1 regulates germ cell transepithelial migration by polarizing germ cells and regulating the localization of DE-cadherin. To test this hypothesis we will first determine the extent of germ cell polarization by Tre1 using ultra structural analysis and immunohistochemistry in wild type and trel backgrounds. We will also determine if polarization is a direct consequence of restricted Tre1 localization and/or activation. Secondly, we will test whether Tre1 is responsible for directed transport, targeted recycling and/or targeted degradation of DE-cadherin, leading to restricted DE-cadherin localization. Lastly, we will perform structure-function analysis of DE-cadherin to identify regions of the protein responsible for localization. We will use this region as bait to identify downstream effectors of Tre1 that are responsible for DE-cadherin localization. Through this work we will determine the mechanism by which Tre1 regulates germ cell polarization and DE-cadherin localization, allowing us to characterize a novel role for GPCRs in invasive migration. Germ cells are a special population of cells that are responsible for producing the next generation and as such they have special properties, for instance they are able to migrate through the tissue from one site to another early in the embryo. During cancer, some cells from the primary tumor gain the ability to migrate away from the original tumor and form additional tumors at new sites. By studying the processes occurring in germ cells that allow them to migrate we will be able to uncover how mutations in cancer cells lead to their motile behavior.